99 Merc 90 steady warning alarm on cold engine

My 99 Merc 90 had been sitting up a few months so I decided to run the engine with the water flush attachment. (Something I have done many times). It started fine and after a few minutes I revved the engine in quick pulses to around 3k and back to idle. Suddenly the warning alarm went off on a steady whine. I know it was getting oil b/c the oil resevoir was full and I was getting good white smoke in the exhaust. I checked the water coming from the pee hole and it was still cool. I shut down and tried to start it again in an hour, and as soon as I turn the key, the warning alarm goes off on a steady whine again. I tried again a week later and it still goes off as soon as I turn the key. Anyone have an idea what is wrong and how I can fix it.<br /><br />Thanks in advance,<br /><br />Scott

Re: 99 Merc 90 steady warning alarm on cold engine

Three possibilities. A bad warning module, the device that separates overheat and low oil warnings and sounds the horn accordingly. A bad overheat sender on the cylinder head, especially if it ever overheated. A short to ground on the tan/blue wire coming from the overheat sender.<br /><br />Addendum:<br />Fourth possibility...bad warning horn. I think that when these fail, the horn sounds. I know that's the case with that "other" American outboard brand.

Re: 99 Merc 90 steady warning alarm on cold engine

You said it sat up for a few months, when was the water pump impeller changed? The impeller could have take a set and is not able to provide enough cooling to the powerhead. Just another thing to think about.

Re: 99 Merc 90 steady warning alarm on cold engine

Thanks guys for the quick responses. dilligaf, I am pretty sure it is not overheating as the alarm goes off immediately and the impellar was just replaced about 4 months ago. WillyBWright, is there an easy way to determine which of the scenarios you mentioned might be the problem. I have a Clymer's manual that I can use as reference, but there is not much in there about the warning alarm.<br /><br />Thanks again,<br /><br />Scott

Re: 99 Merc 90 steady warning alarm on cold engine

SSP,<br /><br />I'm not sure on the older Clymer manuals, but if you have the one for 1998 to 2002 models there is a test procedure listed for this problem. the other possibility which I did not see mentioned and which i have seen on several occasions is a fault in the oil level sensor unit, what happens is the glue on the contact (sender) attached to the oil level float fails and allows the contact to fall to the bottom of the tank and close the circuit with the sensor in the base of the float level switch, this results in a constant horn alarm (not beeps) when the ignition key is turned to the on position without even starting the motor. In a lot of cases I have seen the float switch removed, the sender unit cleaned throughly and reglued with no further problems.<br /><br />Bob

Re: 150 Merc 2004 steady warning alarm

Re: 150 Merc 2004 steady warning alarm

My 150 Merc 2004 steady warning alarm comes on when I excelerate. When
I open the oil cap the alarm goes away. It is a steady BEEEEEEEEEEEEEp
It only comes on when I speed up the boat but if I cruise at a low speed I
do not have the problem. The oil is full and the water is coming out with
a steady steam. Any suggestions? Larry Dee

Re: 99 Merc 90 steady warning alarm on cold engine

bobs probably on the right track...sometimes you have to replace the complete tank assy because you cant get to the float assy to repair..